I mostly use primes on my m43 cameras E-PL5 and EM5. The kit zooms stay on my lesser bodies - PL1 and PL2. For my use I appreciate the extra stop and a bit the 12mm f/2, 20mm f/1.7 and 45 mm f/1.8 give me. I mostly use them for indoor candid shots of people. The lenses are small and discreet and give excellent IQ wide open. That extra stop allows me to use lower ISO and/or increase my shutter speed. So for me, selling my primes would be a no-no.

But for you, its sounds as though a single pro-zoom would be a good move. I will probably get the 12-40 myself one day. It really is a personal decision.